The long-term objective of the proposed research is to understand how motor learning normally occurs and to determine how Parkinson's disease affects one's ability to learn new motor tasks. Close to half a million Americans suffer from Parkinson's disease with about 50,000 new cases diagnosed each year. In a recent epidemiological survey it was reported that 15% of the population aged over 65 and more than 50% of those aged over 85 have some Parkinsonian signs. Along with pharmacological and surgical intervention, physical therapy and exercise may be prescribed to improve mobility. It is therefore important to understand how the disease itself may affect the patients' ability to learn a new movement repertoire, if physical medicine and rehabilitation is to be most effective. The specific aims of this proposal are designed to address several hypotheses regarding the way movements are learned and how this process may be impaired in Parkinson's disease. The first aim of the study is to determine the temporal sequence of changes in limb kinematics and electromyographic (EMG) activity that occurs when subjects learn a new motor task at the elbow. The second aim will test the hypothesis that motor learning is invariant; this will be done by studying learning at different joints. A third aim of the project is to study the limb dynamics and EMG activity when subjects learn an isometric task. This will reveal whether the temporal sequence of changes is similar to anisometric movements in a different class of motor behavior. One advantage of studying learning in an isometric task is that since there is no overt movement of the limb, stretch reflexes are not expected to contribute to the muscle control. This is both relevant and important because long-loop reflexes can be abnormal in Parkinsonian patients. The fourth aim of the research will thus be to determine how Parkinsonian patients acquire motor learning in both an isometric and anisometric task. Motor learning will be studied by using a visual step-tracking task. Subjects will make flexion movements about the elbow, wrist or metacarpo-phalangeal joints to superimpose a cursor linked to joint angle (anisometric task) or joint torque (isometric task) onto a target displayed on a computer monitor. The visual display will be reversed to require the subject to developed a visuo-motor transformation in order to achieve skill at the task (i.e. motor learning). The intent is that the data collected in these experiments will provide answers about how motor learning occurs in normal subjects and how Parkinson's disease affects this fundamental process.